Apparatus and method for casting metal

ABSTRACT

The present invention provides a casting apparatus  10 A including a mold  12  having a molten metal inlet  21  at a first end portion of a partition wall  12   a , and an open/close plug  13  for opening and closing the inlet  21  of the mold  12 , the plug  13  being brought into contact with or detached from an inlet-defining wall, in which molten metal  1 ′ is teemed into the mold  12  when the plug  13  is detached from the inlet-defining wall, and teeming of the molten metal  1 ′ into the mold  12  is stopped when the plug  13  is brought into contact with the inlet-defining wall, wherein a member  20  having the inlet-defining wall is separable from the mold  12 , and the member  20  having the inlet-defining wall is removably provided on the mold  12.

DETAILED DESCRIPTION OF THE INVENTION

[0001] 1. Technical Field to Which the Invention Pertains

[0002] The present invention relates to improvement of a casting apparatus including a mold having, at its first end portion, a molten metal inlet, and an open/close plug for opening and closing the inlet of the mold, the plug being brought into contact with or detached from an inlet-defining wall, in which molten metal is teemed into the mold when the plug is detached from the inlet-defining wall, and teeming of the molten metal into the mold is stopped when the plug is brought into contact with the inlet-defining wall.

[0003] 2. Background Art

[0004] Among casting apparatuses of the aforementioned type, the applicant company of the present invention has provided the casting apparatus as disclosed in Japanese Patent Application Laid-Open (kokal) No. 8-155627. The casting apparatus includes, as shown in FIG. 11, a cooling plate A, a mold B, and an open/close plug C, the mold B and the plug C being provided above the cooling plate A. The mold B includes a lower wall B1 and a partition wall B2, and has an opened bottom. A cavity D is defined by the mold B and the cooling plate A which covers the bottom. A hollow-cylindrical upper wall B3 is provided on the peripheral portion of the partition wall B2, and a molten metal inlet E is provided at the center portion of the wall B2. The upper wall B3 constitutes a reservoir G of molten metal F, the reservoir being provided above the mold B. The molten metal inlet E is employed for teeming into the cavity D the molten metal F stored in the reservoir G. The open/close plug C is provided such that the plug is fitted into or detached from the molten metal inlet E. When the plug C is detached from the inlet E, the reservoir G and the cavity D are brought into communication. When the plug C is fitted into the inlet E, communication between the reservoir G and the cavity D is broken. In FIG. 11, reference letter H represents an electric furnace connected to the upper wall B3 of the mold B.

[0005] In the casting apparatus having the aforementioned structure, firstly, a predetermined amount of molten metal F is fed into the reservoir G while the open/close plug C is fitted into the molten metal inlet E. During feeding of the molten metal F, the electric furnace H is operated, to thereby maintain the molten metal F in the reservoir G at a predetermined temperature, and prevent cooling of the molten metal by the lower wall B1. Subsequently, when the open/close plug C is detached from the inlet E, the molten metal F stored in the reservoir G is sequentially teemed into the cavity D, to thereby fill the cavity D with the molten metal F.

[0006] After the cavity D is filled with the molten metal F, the molten metal inlet E is closed by fitting the open/close plug C into the inlet E, and then cooling water is sprayed from a spray nozzle J onto the cooling plate A. Consequently, the molten metal F in the cavity D is sequentially solidified unidirectionally from the lower portion of the cavity to the upper portion thereof. After the entirety of the molten metal F is solidified, when the cooling plate A is moved downward with respect to the mold B, a cast body (cast ingot) K placed on the upper surface of the cooling plate A is removed from the mold B.

[0007] The cast body K produced through unidirectional solidification is of good quality; i.e., the cast body K does not have defects such as casting cavities, shrinkage cavities, pinholes, and invasion of an oxide. Meanwhile, since the upper portion of the cavity D is closed, a consistent amount of molten metal can be teemed into the cavity even if the amount of the molten metal is not measured. Furthermore, a meniscus portion of the molten metal is not greatly curved, and variation in size and weight between the cast bodies K does not become large.

PROBLEMS TO BE SOLVED BY THE INVENTION

[0008] The cast body K produced in the aforementioned casting apparatus is of good quality, and satisfies requirements of the present market in terms of dimensional accuracy and appearance. However, it is obvious that, in the near future, there will be demand for a casting apparatus for producing the cast body K at further high accuracy. Therefore, at present, there must be established a technique for producing the cast body K at high accuracy; i.e., a technique for attaining higher dimensional accuracy of the open/close plug C and the molten metal inlet E (specifically, dimensional accuracy on the order of 1/100 mm). When the open/close plug C is precisely fitted into the inlet E, leakage of the molten metal F into a space between the plug C and the inlet E can be effectively prevented, and formation of casting burrs on the cast body K can be prevented. In addition, when the lower end surface of the plug C is made to be precisely flush with the lower surface of the partition wall B2, there can be prevented formation of a protuberant- or dented-portion on the cast body K, the portion being attributed to a step formed between the plug C and the partition wall B2.

[0009] Among the members constituting the aforementioned casting apparatus, the open/close plug C can be handled as a single member. Therefore, dimensional accuracy of the plug C per se higher than the present level can be attained relatively easily.

[0010] However, the mold B, which includes the partition wall B2 having the molten metal inlet E, the lower wall B1, and the upper wall B3, is a large-sized structure, and thus handling of the mold B is troublesome. Accordingly, enhancement of dimensional accuracy of the inlet E formed in the partition wall B2 of the mold B is very difficult as compared with the case in which dimensional accuracy of the open/close plug C is improved, and thus costs required for forming the inlet E at high dimensional accuracy inevitably becomes enormously high, preventing the inlet E from being formed to have high dimensional accuracy.

[0011] In view of the foregoing, an object of the present invention is to provide a casting apparatus for producing a cast body of high accuracy easily and at low cost.

MEANS FOR SOLVING THE PROBLEMS

[0012] The present invention provides a casting apparatus comprising a mold having, at its first end portion, a molten metal inlet, and an open/close plug for opening and closing the inlet of the mold, the plug being brought into contact with or detached from an inlet-defining wall, in which molten metal is teemed into the mold when the plug is detached from the inlet-defining wall, and teeming of the molten metal into the mold is stopped when the plug is brought into contact with the inlet-defining wall, wherein a member having the inlet-defining wall is separable from the mold, and the member having the inlet-defining wall is removably provided on the mold.

[0013] The mold may include, at its second end portion, forced cooling means, and the molten metal teemed into the mold may be solidified unidirectionally from the second end portion toward the first end portion. The member having the inlet-defining wall may be attached to a hole formed in the mold or to the outer surface of the mold. When the member having the inlet-defining wall is attached to the hole, the member may be fitted into the hole. Alternatively, a screw thread may be formed on the hole and the member having the inlet-defining wall, and the member may be screwed into the hole.

[0014] Each of the mold and the member having the inlet-defining wall is preferably formed from a combination of materials having thermal conductivities for attaining the molten metal teemed into the mold to be gradually solidified while the flat, continuous solidification interface is formed. It is also preferred that the mold and the member having the inlet-defining wall are preferably formed from a combination of materials, such that the thermal expansion coefficient of the member having the inlet-defining wall is equal to or lower than that of the mold. The mold and the member having the inlet-defining wall may be formed from a combination of materials, such that the bending strength of the member having the inlet-defining wall is equal to or higher than that of the mold. In this case, preferably, the member having the inlet-defining wall is formed from a material, such that the bending strength of the member having the inlet-defining wall is equal to or higher than that of the open/close plug.

MODES FOR CARRYING OUT THE INVENTION

[0015] The present invention will next be described in detail with reference to the drawings showing embodiments of the invention.

[0016]FIG. 1 is a schematic representation showing a first embodiment of the casting apparatus according to the present invention. The casting apparatus 10A shown in FIG. 1 is employed for producing a variety of cast bodies, including metallic cast ingot which is used as stock for plastic working, such as cool forging, hot forging, closed die forging, rolling, extrusion, or forming of rolling; and cast product assuming a product shape. Examples of the raw material of the cast body include iron and steel. Preferably, the raw material of the cast body is a non-iron metal such as aluminum, zinc, or magnesium, or an alloy of aluminum, zinc, or magnesium.

[0017] As shown in FIG. 1, the casting apparatus 10A includes a cooling plate 11, a mold 12, and an open/close plug 13.

[0018] The cooling plate 11 is formed from a metal exhibiting excellent refractory characteristics and having high thermal conductivity, such as copper or aluminum; or from a refractory material having high thermal conductivity, such as graphite, silicon carbide, or trisilicon tetranitride. The cooling plate 11 has a circular plate-like shape. A case 14 and a spray nozzle 15 are provided below the cooling plate 11. The case 14 has a bottom-closed hollow-cylindrical shape, and is provided so as to cover the lower surface of the cooling plate 11. The spray nozzle 15 is used for spraying cooling water from spray holes provided at its head end onto the cooling plate 11, and is attached to the case 14 such that the head end portion is provided inside the case 14 and the spray holes face the lower surface of the cooling plate 11. The cooling plate 11, the case 14, and the spray nozzle 15 are connected to a non-illustrated lifting apparatus via the case 14, and can be moved vertically as a unit by means of operation of the lifting apparatus.

[0019] The mold 12 includes a partition wall 12 a assuming a disk shape and having a diameter slightly smaller than that of the cooling plate 11; a hollow-cylindrical lower wall 12 b provided on the peripheral portion of the lower surface of the partition wall 12 a; and a hollow-cylindrical upper wall 12 c provided on the peripheral portion of the upper surface of the partition wall 12 a. The mold 12 is fixedly provided above the cooling plate 11. When the cooling plate 11 is moved downward, the bottom of the mold 12 is opened. When the cooling plate 11 is moved upward, the bottom of the mold 12 is covered with the cooling plate 11, and a cavity 16 is defined by the partition wall 12 a, the lower wall 12 b, and the cooling plate 11. In consideration of the raw material of a cast body 1A to be produced, wettability of molten metal 1′ with respect to the mold, temperature during use of the mold, corrosion resistance of the mold, etc., the material of the mold 12 may be appropriately selected from among a heat-insulating refractory material predominantly containing calcium silicate, calcium oxide, silicon dioxide, aluminum oxide, or magnesium oxide; a refractory material such as silicon nitride, trisilicon tetranitride, trisilicon tetranitride containing boron nitride, silicon carbide, graphite, boron nitride, titanium dioxide, zirconium oxide, aluminum nitride, or a mixture thereof; and a metal such as iron or copper. A passage for discharging air in the cavity 16 to the outside during teeming of the molten metal, the passage not being illustrated in FIG. 1, is preferably provided at an appropriate position of the mold 12.

[0020] A member 20 having an inlet-defining wall is provided at the center of the partition wall 12 a of the mold 12. The member 20 has a hollow-cylindrical shape and includes a flange 20 a on its upper periphery. The member 20 is removably provided in a hole 12 d formed in the partition wall 12 a, such that the lower surface of the member 20 is made to be flush with the lower surface of the partition wall 12 a. The inner wall of the member 20 defines a molten metal inlet 21 around the center axis of the member 20. The molten metal inlet 21 has a lower end portion having a uniform inner diameter, and an upper end portion having an inner diameter which is gradually increased upward and having a sloped inner surface. The angle of the slope is 15-75°, preferably 30-60°. When the angle of the slope is less than 150, smoothness between the sloped surface and the below-described tapered portion 13 a of the open/close plug 13 is lowered. If the angle of the slope is in excess of 75°, when the diameter of a fitting portion 13 b of the plug 13 remains unchanged, the outer diameter of the plug 13 becomes small, and thus the plug 13 encounters difficulty in maintaining satisfactory strength. Similar to the case of the mold 12, in consideration of the raw material of the cast body 1A to be produced, wettability of the molten metal 1′ with respect to the member 20, temperature during use of the member 20, corrosion resistance of the member 20, etc., the material of the member 20 may be appropriately selected from among a heat-insulating refractory material predominantly containing calcium silicate, calcium oxide, silicon dioxide, aluminum oxide, or magnesium oxide; a refractory material such as silicon nitride, trisilicon tetranitride, trisilicon tetranitride containing boron nitride, silicon carbide, graphite, boron nitride, titanium dioxide, zirconium oxide, aluminum nitride, or a mixture thereof; and a metal such as iron or copper. In the first embodiment, the mold 12 and the member 20 having the inlet-defining wall are formed from silicon carbide, and a mold release agent containing 5% water glass is applied onto a junction surface at which the mold 12 and the member 20 are fitted with each other. The position at which the member 20 is provided; i.e., the position at which the inlet 21 is provided, is not necessarily the center of the partition wall 12 a, and the position may be determined in accordance with the shape of a cast body to be produced.

[0021] The open/close plug 13 assumes a columnar shape, and has a diameter larger than that of the lower end portion of the molten metal inlet 21 and smaller than that of the upper end portion of the inlet 21. The open/close plug 13 has, at its lower end portion, the tapered portion 13 a and the fitting portion 13 b. The outer diameter of the tapered portion 13 a is gradually decreased downward. The fitting portion 13 b assumes a columnar shape, and has a size such that the potion 13 b is fitted into the lower end portion of the inlet 21. The open/close plug 13 is provided so as to be moved vertically while the center axis of the plug 13 is coincident with that of the inlet 21. The plug 13 can be moved vertically by means of operation of a non-illustrated plug driving apparatus. The open/close plug 13 is preferably formed from a heat-insulating refractory non-metallic material having high mechanical strength, such as silicon carbide, trisilicon tetranitride, or a mixture thereof. The plug 13 may be formed from a metallic material having no reactivity or very low reactivity with the molten metal 1′, such as iron or cast steel.

[0022] In FIG. 1, reference numeral 17 represents an upper lid for covering the region above the mold 12, and reference numeral 18 represents an electric furnace connected to the upper wall 12 c of the mold 12.

[0023] When the cast body 1A is produced by use of the casting apparatus 10A having the aforementioned structure, firstly, the cooling plate 11 is moved upward by means of the lifting apparatus, to thereby define the cavity 16 by the cooling plate 11 and the partition wall 12 a and the lower wall 12 b of the mold 12. The open/close plug 13 is moved downward by means of the plug driving apparatus, and the fitting portion 13 b of the plug 13 is fitted into the lower end portion of the molten metal inlet 21. Furthermore, the tapered portion 13 a of the plug 13 may be abutted against the sloped surface of the inlet 21.

[0024] In this configuration, the inlet 21 is closed by means of the plug 13, and thus the reservoir 19 defined by the upper wall 12 c, the reservoir being provided above the partition wall 12 a, and the cavity 16 are disconnected from each other. A mold release agent is preferably applied onto a surface of the mold 12, the surface defining the cavity, in order to facilitate removal of the cast body 1A from the mold. In addition, a mold release agent is preferably applied onto the open/close plug 13 in order to prevent reaction between the plug 13 and the molten metal 1′.

[0025] Subsequently, the electric furnace 18 is operated, and then a predetermined amount of the molten metal 1′ is fed into the reservoir 19. The electric furnace 18 is operated in order to maintain the molten metal 1′ in the reservoir 19 at a predetermined temperature and to prevent the molten metal from being cooled by the lower wall 12 b, to thereby enhance the effect of the below-described unidirectional solidification.

[0026] Subsequently, the open/close plug 13 is moved upward by means of the plug driving apparatus, to thereby remove the fitting portion 13 b of the plug 13 from the lower end portion of the molten metal inlet 21.

[0027] At this stage, the inlet 21 is opened, and thus the reservoir 19 and the cavity 16 are brought into communication. Therefore, the molten metal 1′ stored in the reservoir 19 is sequentially teemed into the cavity 16 through the inlet 21, and the cavity 16 is filled with the molten metal. When the open/close plug 13 is moved upward, the cooling plate 11 is preferably heated to at least 100° C. When the temperature of the cooling plate 11 is lower than 100° C., a “blow defect”; i.e., a type of casting defect is formed, which is not preferable. The upper limit of the temperature of the cooling plate 11 is preferably equal to the temperature of the molten metal 1′. Furthermore, in order to prevent formation of the aforementioned “blow defect,” a mold release agent is preferably applied onto the cooling plate 11 in advance.

[0028] After the entirety of the cavity 16 is filled with the molten metal 1′, the molten metal inlet 21 is closed by moving the open/close plug 13 downward, and then cooling water is sprayed from the spray nozzle 15 onto the cooling plate 11. When cooling water is sprayed onto the cooling plate 11, the molten metal 1′ in the cavity 16 is sequentially solidified unidirectionally from the lower portion of the cavity to the upper portion thereof. As described above, the mold 12 and the member 20 having the inlet-defining wall are formed from silicon carbide. Therefore, as shown by means of a dash and two-dotted line in FIG. 1, the solidification interface (boundary surface between the molten metal and the solidified metal) 1 a becomes parallel to the upper surface of the cooling plate 11 and has a flat, continuous surface, and the molten metal is solidified such that the solidification interface 1 a gradually moves upward. Following solidification of the molten metal 1′ in the cavity 16, the cooling plate 11 is moved downward with respect to the mold 12, and the cast body 1A placed on the upper surface of the cooling plate 11 is removed from the mold 12.

[0029] Since the cast body 1A is produced through unidirectional solidification such that the flat, continuous solidification interface is formed, the cast body 1A is of good quality; i.e., the cast body 1A does not have defects such as casting cavities, shrinkage cavities, pinholes, and invasion of an oxide. Furthermore, since the upper portion of the cavity 16 is closed by the partition wall 12 a and the lower end surface of the open/close plug 13, a consistent amount of molten metal can be teemed into the cavity even if the amount of the molten metal is not measured. In addition, a meniscus portion of the molten metal is not greatly curved, and variation in size and weight between the cast bodies 1A does not become large. Spraying of cooling water from the spray nozzle 15 onto the cooling plate is not necessarily carried out after the inlet 21 is closed by means of the open/close plug 13; cooling water may be sprayed from the nozzle 15 onto the cooling plate before the inlet 21 is closed by means of the plug 13; i.e., during teeming of the molten metal 1′ from the reservoir 19 into the cavity 16. When the thickness of the cast body 1A is large, the cooling plate 11 may be moved downward during cooling, and cooling water may be sprayed directly onto the bottom surface of the cast body 1A.

[0030] In the aforementioned casting apparatus 10A, the member having a wall defining the inlet 21 is separable from the partition wall 12 a of the mold 12, and the member 20 having the inlet-defining wall is removably provided on the partition wall 12 a. Therefore, the member 20 can be handled as a single member of relatively small size. Similar to the case of the member 20, the open/close plug 13 can be handled as a single member. Therefore, very high dimensional accuracies of the inlet 21 and the open/close plug 13 on the order of 1/100 mm can be attained, without involving considerably high production costs or troublesome labor. Even when the member 20 and the open/close plug 13 are formed from different materials, and the thermal expansion coefficients of the member 20 and the plug 13 are different from each other, fitting accuracy between the member 20 and the plug 13 can in practice be verified and regulated during operation by heating the member 20 and the plug 13 to a temperature equal to the molten metal. Therefore, further high dimensional accuracy of the inlet 21 and the plug 13 can be easily attained. Consequently, when the open/close plug 13 is moved downward, the fitting portion 13 b is brought into tight contact with the inner wall of the lower end portion of the inlet 21, and leakage of the molten metal 1′ from the reservoir 19 into a space between the plug 13 and the inlet 21 can be effectively prevented. As a result, the following effects, among others, are obtained: formation of casting burrs on the cast body 1A can be prevented; the cast body 1A can be very smoothly removed from the mold, resulting in no casting problems; and a forged product formed from the cast body does not have defects arising from folded and/or stamped burrs on the forged product. In addition, when the open/close plug 13 is moved downward, the lower end surface of the plug 13 is made to be precisely flush with the lower surface of the partition wall 12 a, there can be prevented formation of a protuberant- or dented-portion on the cast body 1A, the portion being attributed to a step formed between the plug 13 and the partition wall 12 a. During operation of the casting apparatus, the difference in diameter of the open/close plug 13 and the member 20 having the inlet-defining wall is 0.10 mm or less, preferably 0.06 mm or less.

[0031] Since the member 20 having the inlet-defining wall can be handled as a single member, the casting apparatus 10A has advantages in terms of maintenance and control, as described below.

[0032] Firstly, when the member 20 having the inlet-defining wall is worn as a result of prolonged use, or when the member 20 is deformed or broken by collision between the member 20 and the open/close plug 13, the worn or broken member 20 can be removed from the mold 12 and exchanged with a new member, without involvement of removal of other members. Therefore, costs required for maintenance of the casting apparatus of the present invention can be considerably reduced as compared with the case of a conventional casting apparatus, in which the entirety of a mold must be exchanged when such a member is broken.

[0033] Secondly, when a cast body including portions having different shapes is produced, costs required for producing the cast body and a space in which the mold 12 is stored can be reduced. For example, as in the case of a casting apparatus 10B according to a second embodiment shown in FIG. 2, when a projection portion 121 is provided on a member 120 having a wall defining a molten metal inlet 121, even if the same mold 12 is used, a cast body 1B, which differs from the cast body 1A in shape, can be produced by exchanging the member 20 having the inlet-defining wall according to the first embodiment with the member 120 having the projection portion 121. Therefore, costs for producing the mold 12 can be greatly reduced, and storage of the mold 12 when the mold is not needed requires no space. In the second embodiment, identical reference numerals are assigned to those members of the casting apparatus which are identical with those of the casting apparatus according to the first embodiment, and detailed description of the members is omitted.

[0034] The aforementioned effects of the present invention are particularly exerted in a casting apparatus 10C of relatively large size that includes a plurality of molten metal inlets 221, the apparatus pertaining to a third embodiment shown in FIG. 3. When a plurality of members 220, each having a wall defining a molten metal inlet 221, are provided, even if the mold 12 is of large size, the member 220 having the inlet-defining wall can be handled as a single member, the inlet 221 can be subjected to working under the same conditions as those in the first and second embodiments, and high dimensional accuracy of the inlet can be attained. When one of the members 220 is broken, only the broken member 220 is exchanged with a new member, without the remaining member(s) 220 being exchanged with a new member. Therefore, the mold 12 and the remaining member(s) 220 can be used continuously, and thus operation costs of the casting apparatus can be greatly reduced. As in the case of the third embodiment, when a plurality of the members 220 are provided in the mold 12, the members 220 may be of identical or different materials. When a plurality of molten metal inlets are provided in the mold, each of the members 220 does not necessarily include one molten metal inlet, and one of the members 220 may include a plurality of molten metal inlets. In the third embodiment, identical reference numerals are assigned to those members of the casting apparatus which are identical with those of the casting apparatus according to the first embodiment, and detailed description of the members is omitted.

[0035] The first, second, and third embodiments employ the mold 12 including the member 20 fitted into the hole 12 d, the mold 12 including the member 120 fitted into the hole 12 d, and the mold 12 including the member 220 fitted into the hole 12 d, respectively. In the present invention, a member having an inlet-defining wall may be provided on a mold by means of another method; for example, as in the case of a casting apparatus 10D according to a fourth embodiment or a casting apparatus 10E according to a fifth embodiment. In the casting apparatus 10D according to the fourth embodiment shown in FIG. 4, a screw thread 12 e is formed on the inner wall of the hole 12 d formed in the mold 12, a screw thread 320 a is formed on the peripheral wall of a member 320 having a wall defining a molten metal inlet 321, and the member 320 is removably attached to the hole 12 d by means of screw engagement. In the casting apparatus 10E according to the fifth embodiment shown in FIG. 5, the upper wall 12 c is separable from the mold 12; the upper wall 12 c includes, at its lower portion, a fixing portion 12 f; a member 420 having a wall defining a molten metal inlet 421 is fitted into the hole 12 d of the mold 12; and the member 420 is sandwiched by the hole 12 d and the fixing portion 12 f. In the casting apparatuses 10D and 10E according to the fourth and fifth embodiments, the aforementioned effects are obtained, and falling of the members 320 and 420 from the mold 12 can be obviated, and thus smooth casting operation can be carried out reliably. In the fourth and fifth embodiments, identical reference numerals are assigned to those members of the casting apparatus which are identical with those of the casting apparatus according to the first embodiment, and detailed description of the members is omitted.

[0036] The first through fifth embodiments employ the members 20, 120, 220, 320, and 420, respectively, each having a size smaller than that of the upper surface of the cavity 16. However, the present invention is not limited to the casting apparatus in which the size of the member having the inlet-defining-wall is smaller than that of the upper surface of the cavity. For example, as in the case of a sixth embodiment shown in FIG. 6, the size of a member 520 having a wall defining a molten metal inlet 521 may be larger than that of the upper surface of the cavity 16. In the casting apparatus 10F according to the sixth embodiment, the aforementioned effects are obtained, and a connection line formed between the mold 12 and the member 520 is not transferred onto a cast body 1F, and thus a cast body 1F of high quality can be produced. In the casting apparatus 10F according to the sixth embodiment, the member 520 has a generally rectangular shape. However, the shape of the member 520 is arbitrary. Even if the member 520 has a columnar shape similar to those employed in the first through fifth embodiments, when the size of the member 520 is larger than that of the cavity 16, the same effects as described above can be expected. In the sixth embodiment, identical reference numerals are assigned to those members of the casting apparatus which are identical with those of the casting apparatus according to the first embodiment, and detailed description of the members is omitted.

[0037] In the first through sixth embodiments, the members 20, 120, 220, 320, 420, and 520 are attached into the hole 12 d formed on the mold 12. However, the present invention is not limited to the casting apparatus in which the member having the inlet-defining wall is attached into the hole formed in the mold. For example, as in the case of a seventh embodiment shown in FIG. 7, a member 620 having a wall defining a molten metal inlet 621 and including the upper wall 12 c may be removably provided on the upper surface of the mold 12. The lower surface of the member 620 and the upper surface of the mold 12 are subjected to polishing by use of abrasive stone or a lathe, so as to enhance adhesion between the member 620 and the mold 12. The flatness of the polished surface is 0.2 mm or less, preferably 0.1 mm or less. The surface roughness (RZ) of the polished surface is 0.5 mm or less, preferably 0.1 mm or less. When the member 620 is attached onto the upper surface of the mold 12, preferably, means for facilitating mutual determination of the positions of the mold 12 and the member 620 is provided. For example, as in the case of the casting apparatus 10G according to the seventh embodiment, a counter-notch portion 12 g is provided on the upper peripheral portion of the mold 12, and a notch portion 620 a is provided on the lower peripheral portion of the member 620, and the counter-notch portion 12 g is fitted into the notch portion 620 a, to thereby determine the positions of the mold 12 and the member 620. indent In this case, the counter-notch portion and notch portion may be provided conversely, or each of the mold 12 and the member 620 may have both a counter-notch portion and a notch portion. Such a counter-notch portion is not necessarily a protrusion formed on the mold 12 or the member 620, and a locating pin may be provided as a counter-notch portion on the mold 12 or the member 620.

[0038] In the aforementioned first through seventh embodiments, the mold 12 and the members having the inlet-defining wall (20, 120, 220, 320, 420, 520, and 620) are formed from silicon carbide. The mold 12 and each of the members 20, 120, 220, 320, 420, 520, and 620 may be of identical or different materials. There will be described conditions for determining a combination of the materials of the mold 12 and each of the members 20, 120, 220, 320, 420, 520, and 620.

[0039] (1) Combination of Material in Consideration of Thermal Conductivity

[0040] In the aforementioned casting apparatus, in consideration of quality of a produced cast body, as described above, unidirectional solidification is preferably carried out such that the flat, continuous solidification interface is formed.

[0041] Therefore, for example, when the cast bodies 1A, ID, and 1E are of uniform thickness as shown in FIGS. 1, 4, and 5, the mold 12 and the members having the inlet-defining wall (20, 320, and 420) are preferably formed from materials of identical thermal conductivity. The materials of the mold 12 and the members 20, 320, and 420 are not necessarily silicon carbide, and may be appropriately selected from among the aforementioned examples of materials. For example, the mold 12 and the members 20, 320, and 420 may be formed from Lumiboard. “Lumiboard” is produced by Nichias Corporation, and predominantly contains calcium silicate.

[0042] In contrast, as shown in FIG. 8, in a casting apparatus 10H for producing a cast body 1H having a large thickness at a portion below a molten metal inlet 21, the portion of the cast body below the inlet 21 is prone to slow solidification. Therefore, when the mold 12 and the member 20 having the inlet-defining wall are formed from materials of identical thermal conductivity, the flat, continuous solidification interface may fail to be formed.

[0043] Therefore, in the case of the casting apparatus 10H shown in FIG. 8, the member 20 having the inlet-defining wall is formed from a material having a thermal conductivity lower than that of the material of the mold 12. When the member 20 is formed from a material having a low thermal conductivity, the flow rate of heat from the molten metal 1′ stored in the reservoir 19 is lowered in the member 20 as compared with other portions of the mold 12, the entirety of the cast body 1H is solidified uniformly, and thus the solidification interface 1 h becomes flat. Specifically, when the mold 12 is formed from silicon carbide (thermal conductivity=75.1 W/mk), the member 20 is formed from trisilicon tetranitride (thermal conductivity=17.4 W/mk). When the mold 12 is formed from trisilicon tetranitride, the member 20 is formed from Lumiboard (thermal conductivity=0.2 W/mk).

[0044] As shown in FIG. 9, in a casting apparatus 10J for producing a cast body 1J having a small thickness at a portion below a molten metal inlet 121, the portion of the cast body below the inlet 121 is solidified quickly. Therefore, the member 120 having the inlet-defining wall is formed from a material having a thermal conductivity higher than that of the material of the mold 12. When the member 120 is formed from a material having a high thermal conductivity, the flow rate of heat from the molten metal 1′ stored in the reservoir 19 is increased in the member 120 as compared with other portions of the mold 12, the entirety of the cast body 1J is solidified uniformly, and thus the solidification interface 1 j becomes flat. Specifically, when the mold 12 is formed from trisilicon tetranitride, the member 120 is formed from graphite (thermal conductivity=167.0 W/mk). When the mold 12 is formed from aluminum titanate (thermal conductivity=1.2 W/mk), the member 120 is formed from silicon carbide.

[0045] (2) Combination of Material in Consideration of Thermal Expansion Coefficient

[0046] When a casting apparatus is assembled, a member having an inlet-defining wall is attached to a hole of a mold at room temperature. However, in practice, during casting operation, the temperature of the mold and the member having an inlet-defining wall becomes high. For example, when casting is carried out by use of an aluminum alloy serving as a raw material, the temperature of the mold and the member having an inlet-defining wall reaches as high as 660° C. Particularly, in a casting apparatus in which a member having an inlet-defining wall is attached to a hole of a mold, when the thermal expansion coefficient of the member having an inlet-defining wall is higher than that of the mold, excess force is applied to the mold during casting operation, and the mold may be damaged by the force. Therefore, in such a casting apparatus in which a member having an inlet-defining wall is attached to a hole of a mold, the member having an inlet-defining wall is preferably formed from a material having a thermal expansion coefficient lower than that of the material of the mold.

[0047] For example, in the casting apparatus 10A shown in FIG. 1, when the mold 12 is formed from silicon carbide (thermal expansion coefficient=4.2×10⁻⁶/° C.), the member 20 having an inlet-defining wall is formed from trisilicon tetranitride (thermal expansion coefficient=3.2×10³¹ ⁶/° C.). In a casting apparatus 10K shown in FIG. 10, when the mold 12 is formed from stainless steel (SUS: thermal expansion coefficient=17.3×10⁻⁶/° C.), a member 720 having an inlet-defining wall is formed from trisilicon tetranitride. In the casting apparatus 10D shown in FIG. 4, when the mold 12 is formed from Sialon (thermal expansion coefficient=3.1×10⁻⁶/° C.), the member 320 having an inlet-defining wall is formed from graphite (thermal expansion coefficient=2.0×10⁻⁶/° C.). In practice, casting was carried out by use of the casting apparatus 10A shown in FIG. 1 in which the member 20 having an inlet-defining wall was fitted into the hole 12 d having an inner diameter of 30 mm, the difference in diameter between the member 20 and the hole 12 d being 0.1 mm. As a result, there arose no problem attributed to the difference in thermal expansion coefficient between the member 20 and the hole 12 d during use of the apparatus 10A. Furthermore, casting was carried out by use of the casting apparatus 10K shown in FIG. 10 in which the member 720 having an inlet-defining wall was fitted into the hole 12 d having an inner diameter of 40 mm, the difference in diameter between the member 720 and the hole 12 d being 0.05 mm. As a result, no problem arose during use of the apparatus 10K. In addition, casting was carried out by use of the casting apparatus 10D shown in FIG. 4 in which the screw threads 12 e and 320 a (M40-pitch: 2 mm) were formed on the hole 12 d of the mold 12 and the member 230 having an inlet-defining wall, respectively, and the member 230 was screwed into the hole 12 d. As a result, no problem arose during use of the apparatus 10D. “Sialon” is produced by Hitachi Metals, Ltd., and predominantly contains a mixture of aluminum oxide and silicon nitride.

[0048] (3) Combination of Material in Consideration of Bending Strength

[0049] When the inner wall or the sloped surface of a member having an inlet-defining wall is worn, deformed, or damaged through opening/closing operation of an open/close plug, the plug does not operate well, and molten metal leaks through a space between the plug and the member having an inlet-defining wall, since the plug is not tightly fitted into the member. In order to prevent such wear, deformation, or damage, a material of high bending strength is preferably used. However, workability of such a material is poor, and thus costs required for working increases. Therefore, in the aforementioned casting apparatus, preferably, the member having an inlet-defining wall, which is brought into direct contact with the open/close plug, is formed from a material having a bending strength higher than that of the material of the mold, to thereby reduce the frequency of occurrence of the aforementioned wear, deformation, or damage. Particularly, in the casting apparatus 10B shown in FIG. 2 or the casting apparatus 10J shown in FIG. 9, the member 120 having an inlet-defining wall is preferably formed from a material having sufficiently high bending strength and excellent durability, since the member 120 has a complicated shape as compared with those included in the other casting apparatuses of the present invention. The open/close plug, which is brought into contact with the member having an inlet-defining wall, is preferably formed from a material having a bending strength lower than that of the material of the member. For example, in the casting apparatus 10B shown in FIG. 2 or the casting apparatus 10J shown in FIG. 9, when the mold 12 is formed from graphite (bending strength=14.7 MPa), the member 120 having an inlet-defining wall is formed from trisilicon tetranitride (bending strength=392.0 MPa), and the open/close plug 13 is formed from Lumiboard (bending strength=5.2 MPa).

EXAMPLE

[0050] A casting apparatus 10A shown in FIG. 1 was formed by use of a mold 12 formed from silicon carbide and a member 20 having an inlet-defining wall formed from trisilicon tetranitride. By use of the casting apparatus 10A, a cast body 1A (outer diameter: 65 mm, thickness: 10 mm) was formed from JIS 2218 aluminum alloy.

[0051] The mold 12 has an outer diameter of 130 mm, and a height of 200 mm. A partition wall 12 a has a thickness of 30 mm. A hole 12 d has an inner diameter (upper portion) of 80 mm, an inner diameter (lower portion) of 40 mm, and a height (upper portion) of 15 mm. A surface of the mold 12, the surface defining a mold cavity, was subjected to diamond polishing by use of an abrasive plate, to thereby obtain desired flatness.

[0052] The member 20 having an inlet-defining wall has a height of 30 mm, and includes, at its upper portion, a flange 20 a such that the member is fitted into the hole 12 d of the mold 12. A molten metal inlet 21 has an inner diameter of 12 mm, and has, at its upper portion, a sloped surface which is sloped at 450. Before being subjected to firing, the member 20 was roughly profiled by use of a lathe. After being fired, the member 20 was subjected to precise polishing by use of a lathe, an NC milling machine, and an abrasive plate. Particularly, the inlet 21 was subjected to polishing by use of a lathe and an NC milling-abrasive machine, so as to attain a tolerance in diameter of +0.02 mm. When the open/close plug 13 was fitted into the member 20, the difference in diameter between the plug 13 and the inlet 21 (inner diameter: 12 mm) was 0.04 mm.

[0053] The aforementioned processing machine and processing jig used for polishing the member 20 were of small size, and thus the time required for setup of such tools or for polishing the member 20 was shortened, and production cost was relatively low.

[0054] In the manufacture of cast bodies 1A, in substantially 100% of cases, the cast bodies fell spontaneously from the mold 12, and no problem occurred during operation of the casting apparatus, since the dimensional accuracy of the member 20 and the open/close plug 13 was high and leakage of molten metal into a space between the member 20 and the plug 13 was prevented reliably. The resultant cast body 1A did not have-defects on the surface. Therefore, when the as-produced cast body was subjected to forging by use of a forging unit, the forged product did not have defects arising from folded and/or stamped burrs on the forged product.

COMPARATIVE EXAMPLE

[0055] A cast body (outer diameter: 65 mm, thickness: 10 mm) was produced from JIS 2218 aluminum alloy by use of a casting apparatus similar to that employed in the Example. In the casting apparatus of Comparative Example, as shown in FIG. 11, a molten metal inlet E is provided directly in a partition wall B2 of a mold B. The mold B is formed from silicon carbide.

[0056] The mold B has an outer diameter of 130 mm, and a height of 200 mm. The partition wall B2 has a thickness of 30 mm. A surface of the mold B, the surface defining a mold cavity, was subjected to diamond polishing by use of an abrasive plate, to thereby obtain desired flatness. A molten metal inlet E has an inner diameter of 12 mm, and has, at its upper portion, a sloped surface which is sloped at 45°. The inlet E was subjected to polishing by use of a large-sized NC milling-abrasive machine and a large-sized lathe which can support the mold B. However, since the mold B having an outer diameter of as large as 130 mm was supported, rigidity was insufficient, and an accuracy corresponding to tolerance in diameter within a range of +0.2 mm could not be attained. When an open/close plug C was fitted into the inlet E, the difference in diameter between the plug C and the inlet E (inner diameter: 12 mm) was 0.4 mm.

[0057] The aforementioned processing machine and processing jig used for polishing the mold B were of large size, and thus the time required for setup of such tools or for polishing the mold B was about twice the setup time or the polishing time in the Example, and production cost was greatly increased.

[0058] In the manufacture of cast bodies K, only in 72% of cases, the cast bodies fell spontaneously from the mold B, since the dimensional accuracy of the inlet E and the open/close plug C was low, and leakage of molten metal into a space between the inlet E and the plug C was insufficiently prevented. The cast body K that did not fall spontaneously from the mold B had to be removed by subjecting the lower surface of the cast body K to suction by use of a vacuum suction apparatus which was introduced into the casting apparatus.

[0059] As is apparent from the aforementioned results, the casting apparatus of the Example is excellent as compared with that of the Comparative Example in terms of working accuracy and working cost.

[0060] Meanwhile, the costs required for exchange of the member 20 having an inlet-defining wall of the casting apparatus 10A according to the first embodiment shown in FIG. 1, the member 120 having an inlet-defining wall of the casting apparatus 10B according to the second embodiment shown in FIG. 2, the member 220 having an inlet-defining wall of the casting apparatus 10C according to the third embodiment shown in FIG. 3, and the member 620 having an inlet-defining wall of the casting apparatus 10G according to the seventh embodiment shown in FIG. 7 were 20/100, 10/100, 1/100, and 15/100, respectively, with respect to the cost required for exchange of the mold B of the casting apparatus shown in FIG. 11.

[0061] Each of the casting apparatuses according to the first through seventh embodiments is a casting apparatus for producing a cast body having a disk shape. However, the present invention can be applied to a casting apparatus for producing a cast body having another shape; for example, a three-dimensionally profiled cast body. In this case, the shape of a mold, and the position of a molten metal inlet and the number thereof may be appropriately determined in accordance with the shape of a cast body, and are not limited to the aforementioned embodiments. For example, a molten metal inlet is not necessarily provided on a partition wall of a mold, and may be provided on a side wall or at another position of the mold. Each of the casting apparatuses according to the embodiments is a casting apparatus including forced cooling means employing a cooling plate, but the present invention can be applied to a casting apparatus not including forced cooling means. The present invention can be applied to any casting apparatus, so long as the casting apparatus has a structure in which a molten metal inlet is opened or closed by means of an open/close plug. Each of the casting apparatuses according to the first through seventh embodiments employs forced cooling means in which cooling water is sprayed from the spray nozzle 15 to the cooling plate 11, but the casting apparatus may employ another forced cooling means. For example, when forced cooling means in which cooling water is permitted to pass through a passage formed in the cooling plate is applied to the casting apparatus, the direction of the solidification interface of molten metal can be arbitrarily regulated regardless of the shape of a cast body to be produced.

EFFECTS OF THE INVENTION

[0062] As described above, according to the present invention, a member having an inlet-defining wall is separable from a mold, and the member having the inlet-defining wall is removably provided on the mold. Therefore, the member having the inlet-defining wall can be handled as a single member, and the dimensional accuracy of a molten metal inlet can be enhanced without requiring very high working cost and troublesome operation. Consequently, high dimensional accuracy-(i.e., dimensional accuracy on the order of 1/100 mm) of an open/close plug and the molten metal inlet can be attained, and a technique for producing a cast body of high accuracy easily and at low cost can be realized.

[0063] Since the member having the inlet-defining wall is separable from the mold, the casting apparatus of the present invention has advantages in terms of maintenance and control. For example, costs required for exchange of the member having the inlet-defining wall when the member is damaged can be reduced; costs for producing the mold can be reduced; and storing the mold when the mold is not necessary requires no space.

BRIEF DESCRIPTION OF THE DRAWINGS

[0064] [FIG. 1]

[0065]FIG. 1(a) is a cross-sectional view schematically showing a first embodiment of the casting apparatus of the present invention. FIG. 1(b) is a plan view of a mold of the casting apparatus.

[0066] [FIG. 2]

[0067]FIG. 2 is a cross-sectional view schematically showing a second embodiment of the casting apparatus of the present invention.

[0068] [FIG. 3]

[0069]FIG. 3 is a cross-sectional view schematically showing a third embodiment of the casting apparatus of the present invention.

[0070] [FIG. 4]

[0071]FIG. 4 is a cross-sectional view schematically showing a fourth embodiment of the casting apparatus of the present invention.

[0072] [FIG. 5]

[0073]FIG. 5 is a cross-sectional view schematically showing a fifth embodiment of the casting apparatus of the present invention.

[0074] [FIG. 6]

[0075]FIG. 6(a) is a cross-sectional view schematically showing a sixth embodiment of the casting apparatus of the present invention. FIG. 6(b) is a plan view of a mold of the casting apparatus.

[0076] [FIG. 7]

[0077]FIG. 7 is a cross-sectional view schematically showing a seventh embodiment of the casting apparatus of the present invention.

[0078] [FIG. 8]

[0079]FIG. 8 is a cross-sectional view schematically showing an eighth embodiment of the casting apparatus of the present invention.

[0080] [FIG. 9]

[0081]FIG. 9 is a cross-sectional view schematically showing a ninth embodiment of the casting apparatus of the present invention.

[0082] [FIG. 10]

[0083]FIG. 10 is a cross-sectional view schematically showing a tenth embodiment of the casting apparatus of the present invention.

[0084] [FIG. 11]

[0085]FIG. 11 is a cross-sectional view schematically showing a conventional casting apparatus.

DESCRIPTION OF REFERENCE NUMERALS

[0086]1A, 1B, 1C, 1D, 1F, 1G, 1H, 1J, 1K Cast body

[0087]1 a, 1 h, 1 j Solidification interface

[0088]1′ Molten metal

[0089]10A, 10B, 10C, 10D, 10E, 10F, 10G, 10H, 10J, 10K Casting apparatus

[0090]11 Cooling plate

[0091]12 Mold

[0092]12 a Partition wall

[0093]12 b Lower wall

[0094]12 c Upper wall

[0095]12 d Hole

[0096]12 e, 320 a Screw thread

[0097]12 f Fixing portion

[0098]12 g Counter-notch portion

[0099]13 Open/close plug

[0100]13 a Tapered portion

[0101]13 b Fitting portion

[0102]14 Case

[0103]15 Spray nozzle

[0104]16 Cavity

[0105]18 Electric furnace

[0106]19 Reservoir

[0107]20, 120, 220, 320, 420, 520, 620, 720 Member having an fining wall

[0108]21, 221, 321, 421, 521, 621 Molten metal inlet

[0109]620 a a Notch portion 

1. An apparatus for casting an ingot, comprising: a molten metal reservoir positioned at an upper portion, a casting chamber positioned at a lower portion, a partition wall between the reservoir and the chamber, a sprue formed in the partition wall, and an opening/closing plug for opening and closing the sprue and control means for controlling an opening and closing operation of the plug, wherein the casting chamber is defined by a mold comprising a lower mold member a side mold member and the partition wall that constitutes an upper mold member, and at least one of the lower mold member, side mold member and upper mold member comprises a plurality of divided sections that have different shapes from each other in accordance with a shape of a cast ingot and at least one of which is detachable.
 2. An apparatus for casting an ingot according to claim 1, wherein the side mold member comprises a plurality of upper and lower sections, right and left sections and/or oblique sections divided in accordance with the shape of the cast ingot.
 3. An apparatus for casting an ingot according to claim 2, wherein at least one of the plurality of sections of the side mold member is an insert member.
 4. An apparatus for casting an ingot according to claim 1, wherein the lower mold member comprises a plurality of sections divided in accordance with the shape of the cast ingot.
 5. An apparatus for casting an ingot according to claim 4 wherein at least one of the plurality of sections of the lower mold member is an insert member.
 6. An apparatus for casting an ingot according to claim 1, wherein the upper mold member comprises a plurality of sections divided in accordance with the shape of the cast ingot.
 7. An apparatus for casting an ingot according to claim 6 wherein at least one of the plurality of sections of the upper mold member is an insert member.
 8. An apparatus for casting an ingot according to any one of claims 3, 5 and 7, wherein the insert member has a sloped surface for facilitating withdrawal thereof.
 9. An apparatus for casting an ingot according to claim 1, wherein the upper, side and lower mold members are mutually positioned by positioning means.
 10. An apparatus for casting an ingot according to claim 1, further comprising air removing means for discharging air which remains in the casting chamber when molten metal is teemed from the reservoir into the casting chamber via the sprue.
 11. An apparatus for casting an ingot according to claim 10, wherein an inner side surface of the upper mold member defining the casting chamber is sloped upward toward the air removing means.
 12. An apparatus for casting an ingot according to claim 10, wherein an inner side surface of the upper mold member defining the casting chamber is sloped upward toward the sprue.
 13. An apparatus for casting an ingot, comprising a molten metal reservoir positioned at an upper portion, a casting chamber positioned at a lower portion, a partition wall between the reservoir and the chamber, a mold that includes the partition wall, a member with a wall defining a sprue that is detachably attached to the mold, and an opening/closing plug brought into contact with or detached from the sprue-defining wall for opening and closing the sprue, wherein molten metal is teemed into the casting chamber when the plug is detached from the sprue-defining wall, and teeming of the molten metal into the casting chamber is stopped when the plug is brought into contact with the sprue-defining wall, and the mold and sprue defining wall are formed of a material enabling the molten metal teemed into the mold to be gradually solidified while a flat, continuous solidification interface can be formed.
 14. An apparatus for casting an ingot according to claim 13, wherein the mold comprises a lower mold member a side mold member and the partition wall that constitutes an upper mold member, and at least one of the lower mold member, side mold member and upper-mold member comprises a plurality of divided sections in accordance with a shape of a cast ingot.
 15. An apparatus for casting an ingot according to claim 13, wherein the mold (1) is provided at one end portion with forced cooling means so that the molten metal teemed into the casting chamber is solidified unidirectionally from the one end portion toward the other end portion of the mold.
 16. An apparatus for casting an ingot according to any one of claims 13 to 15, wherein the member with the wall defining the sprue (7) is attached to a hole formed in the mold.
 17. An apparatus for casting an ingot according to claim 16, wherein the member with the wall defining the sprue is fitted in the hole when it is attached to the hole.
 18. An apparatus for casting an ingot according to claim 16, wherein the member with the wall defining the sprue and the hole are provided with screw threads and the member is screwed into the hole.
 19. An apparatus for casting an ingot according to any claim 13, wherein the member with the wall defining the sprue is formed on a periphery of the mold.
 20. An apparatus for casting an ingot according to any claim 13, wherein the member with the wall defining the sprue (7) is formed from a first material, the mold is formed from a second material, and the first material has a thermal expansion efficiency lower than that of the second material.
 21. An apparatus for casting an ingot according to claim 13, wherein the member with the wall defining the sprue is formed from a first material, the mold is formed from a second material, and the first material has a bending strength higher that a bending strength of the second material.
 22. An apparatus for casting an ingot according to claim 21, wherein the bending strength of the first material is higher than a bending strength of the plug.
 23. A process for casting an ingot, comprising solidifying molten metal using the apparatus for casting metal set forth in one of claims 1 or 13, from a certain portion of the mold toward a surface of the plug serving as a part of the mold. 